Download Ch. 22 Descent with Modification: A Darwinian View of Life

Objective:
Understand how the mechanism of natural
selection causes evolution.


Bible: Earth is only a few
thousand years old.
Aristotle: organisms don’t
change
◦ Scala naturae: ladder of
increasing complexity


Linnaeus: taxonomy
(naming/classifying
organisms) using genus and
species
Cuvier: paleontologist
discovered the deeper (older)
the rock, the less like modern
organisms fossils look.
◦ Also found extinctions and
speciations.
Gradualism (slow, continuous change)
 Hutton: geologic features explained by graddual
erosion and deposition.
 Lyell: uniformitarianism – same geologic processes
are operating today as in the past, at the same
rate.
◦ Darwin proposed this also happened with organisms.
Lamarck (INCORRECT)
 Use and disuse: body parts used got
bigger/stronger; not used got
small/disappeared.
 These body parts could be passed on to
offspring (inheritance of acquired
characteristics).
Darwin’s Research
 From 1831-6 Charles Darwin traveled the
world on the HMS Beagle.
 Earthquakes moved rocks up Andes
mountains exposing sea creature fossils.
 Finches were unique to islands but also
were found on 2 or more.
◦ They came from S. America and diversified
according to food found on the island they were
on.

Published in 1859 stating:
1. All organisms come from ancestors
2. Mechanism for evolution is natural selection
 Populations change over generations passing beneficial
heritable traits to offspring.


Modifications (adaptations) that helped
organisms survive and have more offspring
with these modifications (descent).
Evolutionary trees could be made showing
where fossils fit in with living organisms.
Sirenia
Hyracoidea (Manatees
(Hyraxes) and relatives)
Elephas Loxodonta Loxodonta
maximus africana
cyclotis
(Africa)
(Asia)
(Africa)
How natural selection works:
 Struggle for existence.
 Individuals survive due to heritable
phenotypic differences.
 These lead to changes in characteristics of a
population over generations.
Artificial Selection
 Humans change organisms by choosing
traits and breeding.
 Led Darwin to believe that natural selection
could work the same over longer periods of
time thus produces drastic changes.
Terminal
bud
Lateral
buds
Brussels sprouts
Cabbage
Flower
cluster
Leaves
Cauliflower
Kale
Flower
and
stems
Broccoli
Stem
Wild mustard
Kohlrabi
Summary of Natural Selection
 Individuals do not change.
 Only works on heritable traits.
 The same trait is not always favorable.
Guppies
 Size and age differences between populations
 Different predators
◦ Killifish: preys on juveniles
◦ Pike-cichlid: preys on mature

Result: sexual maturity in pops with killifish
decreased.

Drug Resistant Bacteria
◦ Staphylococcus aureus is commonly found on people
◦ Became resistant to:
 penicillin in 1945 (2 years after it was 1st widely used)
 methicillin in 1961 (2years after it was 1st widely used)
◦ Methicillin inhibits a protein in bacteria’s cell walls
 MRSA uses a different protein and is now pathogenic.
◦ MRSAs are now resistant to many antibiotics
2,750,000
1
250,000 base pairs
2,500,000
Chromosome map
of S. aureus clone USA300
2,250,000
500,000
Key to adaptations
Methicillin resistance
Ability to colonize hosts
2,000,000
750,000
Increased disease severity
Increased gene exchange
(within species) and
1,000,000
toxin production
1,750,000
1,500,000
1,250,000
Evidence for Evolution
• Homology: similarities resulting from common ancestry
– Comparative Anatomy
– Homologous: same structure different function
– Vestigial: remains of structures that have no current function
– Molecular: same DNA/RNA/amino acids
Human
Cat
Whale
Bat

Homologies
◦ Comparative embryology reveals anatomical homologies
not visible in adult organisms
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
◦ Homologies form nested patterns in evolutionary trees
◦ Evolutionary trees can be made using different types of
data, for example, anatomical and DNA sequence data

Convergent Evolution
◦ The evolution of similar (analogous) features in
distantly related groups
 Analogous traits arise when groups independently
adapt to similar environments in similar ways
◦ Convergent evolution does not provide information
about ancestry
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel

The Fossil Record
◦ The fossil record provides evidence of the extinction of
species, the origin of new groups, and changes within
groups over time
◦ Fossils can document important transitions
◦ EX: the transition from land to sea in the ancestors of
cetaceans
Other
even-toed
ungulates
Hippopotamuses
†Pakicetus
†Rodhocetus
Common
ancestor
of cetaceans
70
60
50
40
30
20
Millions of years ago
†Dorudon
10
Living
cetaceans
0
Key
Pelvis
Femur
Tibia
Foot

Biogeography: closely related species are
geographically close.
◦ Earth’s continents were formerly united in a single
large continent called Pangaea, but have since
separated by continental drift



Study of molecular basis
of genes and gene
expression
Universality of genetic
code
Conservation of amino
acid sequences in
proteins such as
hemoglobin